Motorola MTP700 Detailed Service Manual page 204

4.2 - 82
Synthesizer & VCO Troubleshooting
Use this test on a unit with the following symptom: no Tx or Rx.
Using a 50-ohm probe on the
spectrum analyzer, check the
LO output at the buffer output
at C728.
Is the frequency
at 969.65MHz?
YES
Is the buffer
output between
-3 and 0dBm?
YES
The unit tested successfully
MTP700 Portable Radio / Detailed Service Manual
TetraCom Commands
> 11 timer on
> freq rx 860
> mode rssi
> main_vco on
> 11 timer off
NO
Check the VCO output
at C709, is the freq
969.65MHz?
Check for opens, shorts,
NO
or missing components in
the buffer circuits.
Also check for 4.5Vdc on
L703.
NO
Test the VCO control
voltage at TP700. The
typical range is 0.2 to 4.9V.
YES
Possible prescaler
feedback problem:
1. Check soldering of
C718.
2. Probe to determine
if LO is reaching the
prescaler input.
TRANSCEIVER 800 MHz
Is the control
voltage railed to
NO
<0.2V or >4.9V
Note: This is
YES
the abnormal
condition.
A